Telephone circuit



May 28, 1940. w; KOENlG. JR I 2, 8

TELEPHONE CIRCUIT Filed Feb. 24, 1959 RECEIVER TRANSMITTER CENTRAL OFFICE LOOP A TTOR/VE V Patented May 28, 1940 UN TED sTAT s OF E.

v TELEPHONE CIRCUI 7 Walter Koenig, .Jr.-, Olifton, N. J.,."assignor to 1. Bell Telephone Laboratories,

Incorporated,

' New York, N. Y., a- ;corporation, of New York Application February 24, 1939, serial o. 258,130

4 Claims. (c1. ria -'31 This invention relates to telephone, circuits and, more particularly, to substation circuits for telephone sets including a hand telephone having transmitter and receiver units connected to the subset by a multiconductor cord, one of the conductors being connected to both of the telephone units, Y 7

In telephone .substation circuits, a non-linear resistance. element, such as a. copper-oxide re'ctifier, may be utilized to protect the receiver from: currentsaresulting. from unduly high voltages, transient 'or otherwise, impressed upon or in duced in the telephone line. The non-linear resistance element should be located ina branch of the telephone circuit where it may be effective to protect the receiver but will have no appreciable effect upon the energy transmitted from the telephone'set. A satisfactory arrangement is obtained in telephone-sets'having an anti-side tone circuit byconnecting the non-linear resistance element in the receiver mesh of the circuit. ,However, it has been found that in sets whereinjthere is aqconductor common to the receiver and transmitter units of the hand telephone, a direct current potential drop occurs in this common conductor so that the non-linear linear resistance is substantially or entirely pre-.

vented.

The invention and the foregoing and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. 1 is a circuit diagram of a telephone circuit illustrative of one embodiment of this invention; and v Fig. 2 is a diagram of a portion of the substation circuit illustrated in Fig. 1 with the various impedances rearranged in more conventional bridge formation to facilitate understanding of this invention. I

Referring now to the drawing, the substation circuit, shown to the right of the loop in Fig. 1,

is of the anti-side tone typeand comprises the elementsof-a telephone subset, such'asa ringer ID in series withla condenser II and bridged tion coilhaving threewindings l4, l5and I6,"the

' winding 'l'5 ;havin g a resistance R, and a second condenser. ll. A hand telephone l8, forming a i9,.which may be of the bipolar type, and a, transmitter' 20, for example of the carbon granule type, which are connected to the subset by a cord receiver as showr cateda battery .24 for supplying direct current .to-jthe telephone-set, a 1 U To protect the receiver 19 from; currents rej sulting from unduly high voltages, transientror otherwise, which may appear in the telephone line 12,13, a non-'linear resista'nce element 25 'llfhe substation circuit is-connected through the I -loop -to the central omce atwhich there is;

acrcssthe line conductors l2 and I3, an inducpart of thetelephone' set, comprises a receiver i0 having. threeconductors 2|, 22 and 23, the conductor- 22 beingcomrnon tothe transmitter and is: provided in shunt with the" receiver l9 as v shown.- Theelement 25 may be composed, for example, of a pair of copper-oxide'rectifiers con- Such an element, "as is known, has a very high resistance when nected in opposing multiple.

relativelylow voltages are'im'pressed across the terminalsthereof and has a relatively low resistance at high voltages. Hence, when unduly high voltages appear in the subset circuit, the

resistance element 25 effectivelyprotects the receiver '19 against current surges.

It will be seen that, because of the condenser II, direct current cannot flow in the receiver mesh of the circuit,-that is, through the circuit from battery 24, over line conductor [2, 'windmg 14, cord conductor 22, receiver 19, conductor 23, condenseri'l and line conductor l3 back to the battery 24. However, some current may flow in the transmitter mesh, that is. through the circuit from battery 24, through line conductor I2,:w inding l4, cord" conductor 22, transmitter 20, cord conductor 2| andline conductor l3 back I to thebattery 24. Hence, because of the potential drop in the common conductor 22, abias will be placed across the non-linear resistance element 25. I f

In accordance with one feature of this'invention, such a bias is minimized or eliminated by providing an auxiliary resistance 26 in the substation circuit. .As shown clearly in Fig. 2, this resistance 26. forms one arm of a Wheatstone bridge, the other arms being the winding I5,R, the resistance, RR, of the receiver l9, and'the The so that for normal conditions no bias appears across the non-linear resistance element 25.

It will be noted that although the bridge arrangement balances out direct current bias, it does not balance out speech currents, so that for the latter the element 25 is efiectively connected across the receiver l9 and the winding I5.

Although a specific embodiment of the invention has been shown and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. A telephone circuit comprising a pair of line conductors, a transmitter, a receiver, a connection from one terminal of said transmitter to one or said line conductors, a connection from one terminal of said receiver to the other of said line conductors, a common resistive connection between the other terminal of said receiver and transmitter, a non-linear resistance element connected between said second connection and said resistive connection, and means including a resistance connected between said other line conductor and the point of connection between said non-linear resistance and said common connection for neutralizing the potential drop in said common connection.

2. A telephone substation circuit comprising a pair of line conductors, a transmitter, a receiver, means including three conductors connecting said transmitter andreceiver to said line conductors and forming transmitter and receiver circuits having a common branch including one of said conductors, said receiver circuit having a blocking condenser therein, a nonlinear resistance element in shunt with said receiver and connected to said common conductor,

and means for balancing out the direct current potential drop in said common conductor comprising a resistance connected in said common branch.

3. A telephone circuit comprising a pair of line conductors, means for impressing a direct current potential between said conductors, a pair of series circuits connected across said conductors, one of said circuits including a transmitter, a receiver and a resistance, said receiver being between said transmitter and said resistance, the other of said circuits including said transmitter and a pair of resistances, said re ceiver and said first and pair of resistances constituting arms of a balanced Wheatstone bridge, and a non-linear resistance conected between the common terminal of said pair of resistances and the common terminal of said receiver and said first resistance.

4. A telephone substation circuit comprising a pair of line conductors, a transmitter, a receiver, a three-conductor cord one of the conductors of which is common to said transmitter and receiver, and the other two of which are individual to said transmitter and receiver, an induction coil having a resistive Winding in series with one of said iine conductors, the transmitter conductor being conected to the other of said line conductors and the receiver conductor being connected to one terminal of said winding, a balancing resistance connected between said common conductor and the other terminal of said'winding, and a non-linear resistance connected across said balancing resistance and said Winding, said balancing resistance having a value substantially equal to where R is the resistance of said winding, R0

is the resistance ofsaid common conductor, and RR is the resistance of said receiver.

WALTER KOENIG, JR. 

